It's hard to find any hosted e-mail solution that provides 10gb of storage -- most hosted Exchange solutions run about $10 per month for 500mb-1gb of storage. If you didn't want to access your mail via the web interface, you could always use an application that can access POP3 -- if you used Thunderbird you would get the same relative experience across all platforms and pay nothing; if you run a Windows environment, Outlook Express would work fine and it's built into Windows at no additional cost; in OSX you could use Mail, which is built into OSX and has no additional cost. The nice part about the Google service is that you will always have the web interface for access outside of work and even if you do use a desktop client, you can leave original messages on the Google server to allow for easy searching and archiving. Try to find a hosted solution that gives you 10gb of mail sotrage for less than $5 per month with 99.9% uptime and you're not likely to find many providers.
Many third party hosting companies offer ActiveSync or GoodLink or Blackberry support for a hosted mailbox for an additional monthly charge per seat -- it seems to average an additional $10-$15 per seat per month. Google provides POP3 access to your mail, meaning you can configure your Blackberry Internet Service (BIS) to POP in and grab your mail (usually non-Exchange Blackberry plans are cheaper per month anyway), you can forward your mail using the built-in Google forwarding to the Blackberry address provided by your carrier (i.e., firstname.lastname@example.org), you can use your Windows Mobile e-mail client to POP in and get your mail, and/or you can download and use the free Google Mobile Java application on any Java-capable phone (Blackberries and Windows Mobile devices included). Imagine being able to deploy mobile e-mail access to everyone in the organization at zero cost -- even the receptionist with a RAZR could access his e-mail from his phone.
The online Google Calendar with sharing allows the same kind of functionality as Outlook's calendaring application, but it does not yet have good integration with a desktop application. SpanningSync for OSX is the best 2-way sync between iCal and Google Calendar, but there does not seem to be a great solution for other desktop clients and other operating systems. Mozilla does have some calendar projects that are worth evaluating and hopefully someone will create a 2-way sync for all platforms using one of the Mozilla products.
While nice to have and be able to manage from within the mail interface, it would probably take a policy statement in order to make employees that are used to using AIM or Skype to switch to Google Talk. I would implement it as an internal-only instant messaging protocol and let employees use other methods and applications to chat with people outside the company.
Global Contact List
The administrator console makes it pretty easy to set up and share global contacts.
It's simply not yet implemented in Google Calendar -- they need to get it implemented quickly.
Docs and Spreads
The per seat cost of Word and Excel vs. paying nothing for Docs and Spreads makes this a no-brainer for most small businesses. Furthermore, the sharing and revision control along with the centralized off-site storage of documents and spreadsheets would be very attractive to me. The Google products don't do everything quite as well as Word and Excel, but you can't beat the price and I would rather have a small business using Docs & Spreads than looking at an OpenOffice deployment (note: I'm a big fan of OpenOffice and similar products, but I think that many small business employees would be perfectly well served with Docs & Spreads). The glaring hole right now for Google's business applications is a PowerPoint competitor, but rumor has it that they should be launching that product shortly.